It said aid agencies and international donors had failed to address the shortages, putting additional lives at risk in a country where civil war has killed tens of thousands and left millions homeless and starving.

“On top of this already dire humanitarian situation, an additional and preventable medical emergency is unfolding,” MSF president Joanne Liu wrote in an open letter.

Liu said there were “unacceptable and devastating outages of drugs throughout the country” after a donor-backed programme known as the Emergency Medicines Fund was handed over to the government and subsequently collapsed.

“A new rainy seas is approaching fast, promising new outbreaks as well as complicated logistics,” Liu said.

One of the world’s least developed nations, South Sudan won independence from Sudan in 2011 but two years later a new civil war began, pitting President Salva Kiir against his former deputy Riek Machar.

The conflict has been characterised by human rights abuses, attacks on civilians, ethnic massacres and widespread rape. At least 50,000 people have been killed, 2.4 million have been forced from their homes and 2.8 million need emergency food to survive.